Greater attention is being focused on the mechanism of action of neurohormones, with particular emphasis on the relationship between hormonal receptors and adenylate cyclase. Genetic analysis and subcellular biochemical analysis of cyclic AMP metabolism and hormone binding activity in hybrid somatic cells is being utilized as a technique that may yield fundamental information on the nature of the receptor-cyclase interaction and the genetic mechanisms controlling the expression of these components. Effects of adenosine and analogs are being examined on brain slices, primary fetal brain cultures, and established neuronal and non- neuronal cell lines. The metabolism and actions of 2-C1 adenosine are being studied in detail as a means of studying the mechanism of action of such compounds. Effects of PGE1 on cyclic AMP accumulation in brain are being described. Bacterial toxins are also being utilized to influence cyclic AMP in cultured cells, since these compounds appear to regulate cyclic AMP metabolism by mechanisms distinctly different than those utilized by hormones.